Carbon source-regulated anaerobic phosphate reduction in a bioelectrochemical system for low-carbon wastewater treatment: Process and mechanism

Gaseous phosphine (PH3) formation via biological phosphate reduction represents a promising pathway for advanced phosphorus removal from wastewater, yet its application in low‑carbon influents is severely constrained by limited electron donor availability. Using raw wastewater with a background COD of 86–102 mg l-1, sodium acetate (199 mg COD l-1) was compared with glucose at two supplementation levels (203 and 366 mg COD l-1) in bioelectrochemical systems (BES), alongside a non‑current glucose control (T0). The glucose‑fed systems at moderate dosage (T2, 203 mg COD L-1) yielded average PH3 concentrations of 27.4 μg m-3, representing 2.01‑ and 1.71‑fold increases over acetate‑fed (T1) and non‑current (T0) systems, respectively, indicating that complex carbon substrates more effectively promote phosphate reduction. However, excessive glucose (T3, 366 mg COD L-1) diverted additional electrons toward competitive methanogenesis and sulfate reduction, lowering PH3 production to 19.8 μg m-3 despite greater organic carbon availability, suggesting that moderate dosage may provide a favorable balance of electron supply to enhance phosphate reduction. Mechanistically, glucose fermentation sustained higher electron transport system and alkaline phosphatase activities, generating abundant reducing equivalents ([H]) that drove enzymatic phosphate reduction, while enriching carbon‑metabolizing genera (Candidatus Competibacter, Denitratisoma) and upregulating pst‑associated phosphate transport genes. This work suggests that carbon‑source regulation may modulate the competitive utilization of reducing power, favoring phosphate reduction over competing pathways, thereby offering practical guidance for achieving gaseous‑phase phosphorus removal in carbon‑deficient wastewater treatment.